This invention relates to a steer-by-wire system, and more particularly to a steer-by-wire handwheel actuator.
It is known in the art to have a steering system with mechanical linkage from the steering wheel to the steerable road wheels. Even with power assist, the driver of a mechanically linked vehicle can feel the forces of the road against the steerable wheels through the steering wheel. Indeed, this is a desired feature of direct linkage and is sought out by purchasers of high performance vehicles in the form of so-called xe2x80x9crack-and-pinionxe2x80x9d steering. The road forces felt in the steering wheel give the driver feedback he can use to anticipate and control the vehicle, or at least create the comfortable feeling that he is in control of the vehicle. Remove this feedback, such as in the case of xe2x80x9cmushyxe2x80x9d power steering, and the driver will have the uncomfortable feeling of being separated from the road wheels, not quite in control, and will tend to oversteer his vehicle, particularly in demanding situations such as sharp or sudden turns.
By definition, a steer-by-wire system has no mechanical link connecting the steering wheel from the road wheels. In effect, the steering wheel is little more than a joystick, albeit an extremely sophisticated joystick. Exemplary of such known steer-by-wire systems is commonly-assigned U.S. Pat. No. 6,176,341, issued Jan. 23, 2001 to Ansari, which is wholly incorporated herein by reference. What is needed is to provide the steer-by-wire driver with the same xe2x80x9croad feelxe2x80x9d that a driver receives with a direct mechanical link. Furthermore, it is desirable to have a device that provides a mechanical back up xe2x80x9croad feelxe2x80x9d in the event of multiple electronic failures in the steer-by-wire system. In addition, a device that provides positive on-center feel and accurate torque variation as the handwheel is rotated is also desirable. Existing steer-by-wire devices produce excessive lash, excessive noise and insufficient over-load torque capability as the handwheel is rotated to its end of travel in either direction.
A steer-by-wire steering system is defined as a steering system with no mechanical connection between a steering wheel and a set of steering gears or actuators. Such systems are advantageous because they permit auto and other vehicle designers great latitude in use of space that would normally be taken up by mechanical linkages, among other reasons.
In an exemplary embodiment of the invention, a steer-by-wire handwheel actuator is described, which provides feedback of road forces to the operator of a steer-by-wire vehicle. A handwheel actuator comprises a driver input shaft; a gear train connected to the driver input shaft; a motor responsive to control signals from a controller and connected to the gear train; an electro-mechanical brake responsive to the control signals from the controller and connected to one of the driver input shaft and the gear train; and a stop mechanism attached to a housing and coupled to one of the electro-mechanical brake and the gear train.